1. Field of the Invention
The invention described herein relates to assessment of medical conditions, and more particularly to the assessment of neurological conditions through statistical methods.
2. Related Art
It is well known that neurological anomalies can be reflected in the electrical activity of the brain. Such electrical activity is therefore commonly used to diagnose a variety of neurological disorders or to evaluate the treatment thereof. Electrical activity in the brain is typically captured and analyzed in the form of an electroencephalograph (EEG).
Neurological diagnosis using EEGs has a number of drawbacks, however. An EEG, when viewed as a waveform, can only be analyzed with respect to frequency and power. An EEG cannot be analyzed in the time domain given that an EEG represents brain activity uncorrelated to any particular event in time. Moreover, EEGs tend to have significant variance over multiple trials even when performed on the same individual. This is due, in part, to the tendency of patients to react to ambient stimuli while the EEGs are being taken. In addition, EEGs, as signals, tend to have a low signal to noise ratio (SNR). Once collected, EEGs are difficult to analyze because of these factors. Analysis of EEGs by medical personnel tends to be difficult and time consuming.
Because of the difficulties in performing EEG analysis, the use of evoked response potentials (ERPs) has been proposed. An ERP represents neural electrical activity that occurs as a result of a specific sensory stimulus to the patient, such as a flash of light or a tone. The electrical activity, measured as voltage (that is, potential), is therefore an evoked response to a stimulus. Like an EEG, an ERP is typically collected and analyzed as a waveform. Unlike an EEG, however, an ERP can be analyzed in the time domain as well as the frequency domain. ERPs also tend to be less variable than EEGs over multiple trials on a given patient. Nonetheless, as in the case of EEGs, artifacts occur in ERPs and their removal is difficult and error-prone. Noise reduction is also difficult. The use of ERPs as a diagnostic tool is thus expensive and time consuming. Attempts to automate ERP processing have not been widely successful.
Hence there is a need for a method of assessing the neurological condition of a patient, where the method obtains and processes relatively consistent, low noise, artifact-free data. Moreover, the diagnostic method must be fast, inexpensive, and reliable.